[CSGen] Closure analyzer shouldn't walk into local some decls/patterns

While trying to gather all references to external variables,
analyzer shouldn't walk into patterns and any local declarations
except to pattern bindings, because decls do not participate
in inference and patterns cannot contain references analyzer
is looking for.

Author: xedin

lib/Sema/CSGen.cpp

@@ -2941,6 +2941,14 @@ namespace {
 
           return Action::Continue(expr);
         }
+
+        PreWalkAction walkToDeclPre(Decl *D) override {
+          return Action::VisitChildrenIf(isa<PatternBindingDecl>(D));
+        }
+
+        PreWalkResult<Pattern *> walkToPatternPre(Pattern *P) override {
+          return Action::SkipChildren(P);
+        }
       } collectVarRefs(CS);
 
       closure->walk(collectVarRefs);